Spark plug



Dec. 9, 1941.

D. H. CORBIN ETAL SPARK PLUG Filed March 31, 194].

llws/vrans.

- ATromvsya I ceramic material.

'Pa'tented Dec. 19.41

SPARK PLUG Douglas Haynes Corbin, Dunstable, and Robert Ross Barrington, Luton, England, asslgnors to General Motors Corporation, Detroit, Mich., a

corporation of Delaware Application March 31, 1941, Serial No. 386,184 In Great Britain March 29, 1940 7 Claims.

firmly attached to the insulator in sealed relation.

The coeificients of expansion of the ceramic material when fired, and the conductive material, should be approximately equal.

The accompanying drawing illustrates two steps in the making of a spark plug according to the invention and they will be referred to in the description which follows.

On the insulator 11 shown in Figure 1 three pellets are placed ready for insertion in a moulding press. The insulator a is made of a mixture of highly refractory oxides such as alumina, and a temporary binder. The outer pellet b is formed of finely divided platinum powder with sufiicient quantity of a binder, such as a synthetic resin, to make it mouldable. The pellet c is made up of two parts of finely divided platinum powder, one part ceramic material similar to'that forming the insulatonand a small quantity of a binder. The third pellet d which fits in the preformed I end of the insulator bore is made of the same mixture as pellet 1), although the proportion of cefamic materialjpan be increased if desired. The assembly is ;then put in a moulding press may be any conductive metal or metallic compound such as a carbide oxide, in finely divided form, which will resist erosion and corrosion, and which has a coefiicient of expansion close to that of the ceramic constituent. Some of the nonmetallic carbides, such as those of boron and silica, or a metallic carbide such as tungsten carbide may be used. The noble metals and particularly platinum and those of the platinum group and alloys thereof are preferred. (A platinum-iridium or platinum-rhodium alloy can be used.) Some of these metals may be used in the oxidised state.

The form of the spark terminal of the electrode, made from the mixture, can be varied. For example it may consist of a series of terminal areas of small channels leading into the central bore. The means of connecting the terminal to the main, enclosed part of the central electrode is designed according to the shape thereof and any practical requirements that may have to be fulfilled.

What we claim and desire to secure by Letters Patent is:

1. A spark plug in which at least that part of the central electrode which forms a spark terminal is fused to the insulator by a mixture of ceramic and conductive materials.

2. A spark plug in which the central electrode tip which forms the spark terminal is connected to the insulator by one or more intermediate layers of mixtures of ceramic and conductive having dies of llsuch a shape as to bring the assembled pellets and insulator to the shapes shown in 2. This forming operation forms the pellets c and d into one single mass.

The assembly is then heated up to about 950 to drive off the binder. After this it is fired at about 1700 C. according to the nature of the This firing forms the insulator into a .dense non-porous body, and the pellets c, d are similarly aifected so that the central bore of the insulator is sealed in a gastight manner. Due to the presence of the metal, it is conductive, and therefore is in electrical connection with the outer. pellet b which, due to the firing, has been sintered to a metallic layer.

The central electrode is then cast or inserted in the bore of the insulator and fixed in position in any of the'usual ways.

The conductive constituents of the mixture materials sintered to the insulator. I

' 3. A spark plug in which the central electrode tip which forms the spark terminal comprises a layer of sintered metal, and at least one layer of sintered metal and ceramic material between it and the insulator, the layers forming a gas tight seal for the central bore of the insulator.

4. A spark plug comprising an insulator formed of one or more refractory oxides such as alumina sintered into a dense non-porous condition, and a central electrode whose sparking terminal is formed of one or more metals of the platinum group, joined to the insulator in ga's-tight relationship by one or more layers of mixtures of such oxides and such metals sintered in situ.

5. A method of making a spark plug which comprises closing the end of the insulator central bore with layers of finely ground material, the outer layer being electrically conductive and the other layer or layers being a mixture or mixtures of metal and ceramic material, and then firing the insulator to a dense non-porous condition and at the same time sintering said layers so as to fuse them together and to the insulator in a gas-tight manner.

6. A spark plug in which the central electrode tip which forms the spark terminal comprises a layer of sintered metal, and at least one layer of sintered metal and ceramic material between it and the insulator, the layers forming a gas tight seal for the central bore of the insulator,

' said layers having approximately the same coeflicient of expansion as the insulator.

'7. The method of making a spark plug which comprises closing the firing end of the insulator bore with a compacted, finely ground mixture of electrically conducting, heat resistant material and a binder, such as a synthetic resin, firing the insulator to drive off the binder, and thereafter firing the insulator to a dense, non-porous condition and at the same time sintering the conducting materials together and to the insulator to seal the bore.

DOUGLAS HAYNES CORBIN. ROBERT ROSS HARRINGTON. 

